Fuel price

H

Hugh Jass

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What is the fuel price for 93 unleaded supposed to be? R9.96 IIRC.. I just paid R9.70 a litre.

What are you paying?
 
at the moment I don't care.. Nothing I can do about it, beside hand over my monies :(
 
Filled up my tank and it cost me over R700.
Good thing I only do around 500km a month...
 
nakedpeanut said:
lol i barely use my breaks! I gear down and take ages to stop over a distance :D irritates the heck out a people
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Let me get this straight. You think by using the engine braking method you are actually saving petrol as opposed to when you just brake with zero throttle? :wtf:

Me thinks you watched too much top gear
 
rakabos3 said:
Let me get this straight. You think by using the engine braking method you are actually saving petrol as opposed to when you just brake with zero throttle? :wtf:

Me thinks you watched too much top gear
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My assumption is that by breaking with the engine, I am using my momentum and gears to turn the engine over so it uses minimal - no petrol.
As opposed to cruising up to lights then hitting breaks and sitting idle there?

I feel like i save petrol therefor it is true :p hahaha but correct my logic if i'm wrong.
PS it is a vw polo 06
 
nakedpeanut said:
My assumption is that by breaking with the engine, I am using my momentum and gears to turn the engine over so it uses minimal - no petrol.
As opposed to cruising up to lights then hitting breaks and sitting idle there?

I feel like i save petrol therefor it is true :p hahaha but correct my logic if i'm wrong.
PS it is a vw polo 06
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I'm sure you use more fuel with engine breaking as the revs shoot up when gearing down.
High revs = eats more fuel.
 
SaiyanZ said:
I'm sure you use more fuel with engine breaking as the revs shoot up when gearing down.
High revs = eats more fuel.
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but i'm not putting my foot on the gas. Thus the engine does not require any fuel to turn over due to my momentum. But if I was stationary and it was idling then it would require fuel to turn over the engine so that it does not stall....
Where's a proper engine guru to answer this?
 
SaiyanZ said:
I'm sure you use more fuel with engine breaking as the revs shoot up when gearing down.
High revs = eats more fuel.
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Not when it's your momentum that provides the power for that revs. High revs = eats more fuel when you're accelerating by using the throttle.

nakedpeanut said:
My assumption is that by breaking with the engine, I am using my momentum and gears to turn the engine over so it uses minimal - no petrol.
As opposed to cruising up to lights then hitting breaks and sitting idle there?
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The engine will keep turning if you leave the car in fifth gear and use your brakes to stop. It comes down to a choice between putting strain on your gears to stop or using your brakes. I choose the brakes.

Either way, your minimizing your gas usage by not accelerating towards a stop or red traffic light like an idiot.
 
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nakedpeanut said:
but i'm not putting my foot on the gas. Thus the engine does not require any fuel to turn over due to my momentum. But if I was stationary and it was idling then it would require fuel to turn over the engine so that it does not stall....
Where's a proper engine guru to answer this?
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You are using more fuel at higher RPM's. At 3,000RPM, the intake valve is opening and closing TWICE as many times as it is at 1,500RPM, so more fuel is being pulled into the combustion chamber.

Use your brakes to slow down - not your gears. You get less wear and tear on the gearbox, clutch and thrust bearing, and you do save a small amount of fuel.
 
So we are agreed that engine braking saving fuel is the same as looking for fairies and gnomes in your garden lol...
 
So if i'm cruising down a hill with my car in gear (say 4th @3000rpm) with my foot OFF the gas pedal, u guys are saying it is using more petrol?
And thus I should change to 5th so it will decrease the rpm ... and thus my petrol consumption...

I disagree and this is why: http://en.wikipedia.org/wiki/Engine_braking
The term engine braking usually refers to the braking effect caused by throttle position induced vacuum in petrol (gasoline) engines. While some of the braking force is due to friction in the drive train, this is negligible compared to the effect from vacuum.
When the throttle is lifted less air is allowed to pass through the intake manifold, and the engine works against this vacuum. It is the deceleration of the engine against this vacuum which provides the braking effect.
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and

Engine braking passively reduces wear on brakes and helps a driver maintain control of the vehicle. Active use of engine braking (shifting into a lower gear) is advantageous when it is necessary to control speed while driving down very steep and long slopes. It should be applied before regular disk or drum brakes have been used, leaving the brakes available to make emergency stops. The desired speed is maintained by using engine braking to counteract the gravitational acceleration.

Improper engine braking technique can cause the wheels to skid (also called shift-locking), especially on slippery surfaces such as ice or snow, as a result of too much deceleration. As in a skid caused by over-braking, the vehicle will not regain traction until the wheels are allowed to turn more quickly; the driver must reduce engine braking (shifting back up or engaging the clutch on a manual transmission) to regain traction.

Engine braking is intrinsically available in non-hybrid vehicles with gasoline-powered internal combustion engines, regardless of transmission type. In almost all cases, it is active when the foot is lifted off the accelerator, the transmission is not in neutral, the clutch is engaged and a freewheel is not engaged.
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Then I agree with the guy in the comments SonyAD http://www.dailyfueleconomytip.com/driving-habits/fuel-economy-tip-avoid-engine-braking/

Utter nonsense. All modern fuel injected, drive by wire throttle cars have such a thing as throttle position sensor. This tells the Electronic Control Unit whether to and how much fuel to inject. Ignition probably carries on anyway.

Even early fuel injected (single injector, in the intake manifold/plenum) engines that had the throttle actuated directly by the driver, through a cable, didn’t use any fuel if you downshifted without using the throttle. As they had, wait for it, a throttle position sensor as well.

Then again, I always blip the throttle to help the clutch and smooth the downshift. Even so, the amount of fuel burnt is less than dropping to idle and using the brakes. And there’s the added bonus that you can start accelerating right away, should the light turn green, due to being in the appropriate gear from the downshift.

Your advice is at most valid for carburetted cars.

In the future kindly don’t presume to dispense advice on what you don’t have a good enough grasp of yourself.
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And engine braking is easier on the conrods, rod bearings, crank, etc. Because there is no combustion, the most demanding stroke of the cycle.

Also, the main bearings, conrod bearings, etc. don’t care that the momentum is provided by the starter, the flywheel, the road or some other cylinder firing. Except for cylinders which ought to be firing, the forces occur practically the same, due to the flywheel inertia. However, the forces developed on the cylinder head, block, piston, rings, wrist pin, bearings, crank, main bearings, etc. by a cylinder firing are higher than those due to the intake, compression and exhaust strokes.

Which ought to be obvious, since the energy for ther othe strokes comes from the power stroke. Which still has some mechanical energy left over to move the vehicle.

In the meantime, oil is still being pumped through the engine. Because the oil pump likewise doesn’t care whether its internal combustion, flywheel inertia or some external force that is driving the engine.

So, basically, except for rings and maybe piston skirts, the wear arguments are also bollocks.

One more thing, in throttled engines throttling losses also contribute to engine braking. Because you’re basically making the engine pump air against a pressure gradient by restricting it’s air intake.

Please, educate yourselves before presuming to dispense advice or technical opinions on an advanced topic.
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So i'll continue to drive like I do and save brakes and petrol.
 
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genetic said:
You are using more fuel at higher RPM's. At 3,000RPM, the intake valve is opening and closing TWICE as many times as it is at 1,500RPM, so more fuel is being pulled into the combustion chamber.
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Not true.
If you take your foot off the accelerator pedal, the butterfly valve in the throttle body closes which in turns causes the EFI system to reduce the amount of fuel being injected.
Less air going into the cylinders = less fuel being injected.
Without a throttle limiting the air supply the engine would try to red line all the time on it's own.
Revs (and power) are primarily controlled by controlling the air supply - the fuel system just adapts to the air being supplied to either produce max power or run most efficiently (O2 metering, TPS sensor, MAF sensor or a combination of the three).

If power and revs were only controlled by the fuel system (in a Wide Open Throttle situation) then the only way to keep the power and revs down would be to reduce fuel. That in turn would lead to a lean fuel mixture which leads to higher EGT's and can result in detonation (under fueling) and nice stuff like burnt valves and piston tops.

Use your brakes to slow down - not your gears. You get less wear and tear on the gearbox, clutch and thrust bearing, and you do save a small amount of fuel.
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You can save some fuel by down gearing (read reason above) but it's not a lot and the extra wear on the gearbox may out weight the cost of new sets of brake pads.
 
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